scholarly journals Formation of complex molecules in translucent clouds: acetaldehyde, vinyl alcohol, ketene, and ethanol via “nonenergetic” processing of C2H2 ice

2020 ◽  
Vol 635 ◽  
pp. A199 ◽  
Author(s):  
K.-J. Chuang ◽  
G. Fedoseev ◽  
D. Qasim ◽  
S. Ioppolo ◽  
C. Jäger ◽  
...  
Keyword(s):  
Solid State ◽  
Surface Chemistry ◽  
Vinyl Alcohol ◽  
Isotope Labeling ◽  
Early Stage ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Solid State Reactions ◽  
Oh Radicals

Context. Complex organic molecules (COMs) have been identified toward high- and low-mass protostars as well as molecular clouds, suggesting that these interstellar species originate from the early stage(s) of starformation. The reaction pathways resulting in COMs described by the formula C2HnO, such as acetaldehyde (CH3CHO), vinyl alcohol (CH2CHOH), ketene (CH2CO), and ethanol (CH3CH2OH), are still under debate. Several of these species have been detected in both translucent and dense clouds, where chemical processes are dominated by (ground-state) atom and radical surface reactions. Therefore, efficient formation pathways are needed to account for their appearance well before the so-called catastrophic CO freeze-out stage starts. Aims. In this work, we investigate the laboratory possible solid-state reactions that involve simple hydrocarbons and OH-radicals along with H2O ice under translucent cloud conditions (1 ≤ AV ≤ 5 and nH ~ 103 cm−3). We focus on the interactions of C2H2 with H-atoms and OH-radicals, which are produced along the H2O formation sequence on grain surfaces at 10 K. Methods. Ultra-high vacuum experiments were performed to study the surface chemistry observed during C2H2 + O2 + H codeposition, where O2 was used for the in situ generation of OH-radicals. These C2H2 experiments were extended by a set of similar experiments involving acetaldehyde (CH3CHO) – an abundant product of C2H2 + O2 + H codeposition. Reflection absorption infrared spectroscopy was applied to in situ monitor the initial and newly formed species. After that, a temperature-programmed desorption experiment combined with a quadrupole mass spectrometer was used as a complementary analytical tool. The IR and QMS spectral assignments were further confirmed in isotope labeling experiments using 18O2. Results. The investigated 10 K surface chemistry of C2H2 with H-atoms and OH-radicals not only results in semi and fully saturated hydrocarbons, such as ethylene (C2H4) and ethane (C2H6), but it also leads to the formation of COMs, such as vinyl alcohol, acetaldehyde, ketene, ethanol, and possibly acetic acid. It is concluded that OH-radical addition reactions to C2H2, acting as a molecular backbone, followed by isomerization (i.e., keto-enol tautomerization) via an intermolecular pathway and successive hydrogenation provides so far an experimentally unreported solid-state route for the formation of these species without the need of energetic input. The kinetics of acetaldehyde reacting with impacting H-atoms leading to ketene and ethanol is found to have a preference for the saturated product. The astronomical relevance of the reaction network introduced here is discussed.

The Effect of Different Oxidizing Atmospheres on the Initial Kinetics of Copper Oxidation as Studied In Situ UHV-TEM

1999 ◽  
Vol 589 ◽  
Author(s):  
Mridula D. Bharadwaj ◽  
Anu Gupta ◽  
J. Murray Gibson ◽  
Judith C. Yang
Keyword(s):  
Water Vapor ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Solid State Reactions ◽  
Copper Oxidation ◽  
High Vacuum Condition ◽  
Ultra High Vacuum Condition ◽  
Kinetics Of

AbstractEffect of moisture on the oxidation of copper was studied using in situ UHV-TEM. The ultra high vacuum condition is required for minimum contamination effects. The initial observations show that the water vapor reduces the oxide as well as reduces the rate of oxidation if both oxygen gas and water vapor are simultaneously used. Based on these observations, we have speculated on the role of moisture in the solid state reactions involved in copper oxidation

Heteroepitaxy: The Missing Link Between Surface Chemistry and Dry Corrosion

2000 ◽  
Vol 619 ◽  
Author(s):  
Judith C. Yang ◽  
Mridula Dixit Bharadwaj ◽  
Lori Tropia
Keyword(s):  
Electron Microscopy ◽  
Water Vapor ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Solid State Reactions ◽  
Transmission Electron ◽  
Oxygen Gas ◽  
Cu Oxidation

ABSTRACTWe have investigated the initial stages of Cu (001) oxidation in dry and moist oxidizing conditions using in situ ultra-high vacuum (UIHV) transmission electron microscopy (TEM). To investigate the role of moisture in the solid state reactions in Cu oxidation, we have examined the oxidation of Cu (001) with water vapor. Our observation indicate that water vapor causes reduction of Cu2O and retards the oxidation rate if both oxygen gas and water vapor are used simultaneously which contradicts the thermochemical data. We are also modeling the nucleation to coalescence of the oxide scale using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation and have noted a qualitative agreement.

scholarly journals Kinetics of Solid-State Reactions in Ni-Zr Thin Films

1991 ◽  
Vol 230 ◽  
Author(s):  
R. B. Schwarz ◽  
J. B. Rubin
Keyword(s):  
Solid State ◽  
Reaction Rate ◽  
High Vacuum ◽  
Reaction Times ◽  
Ultra High Vacuum ◽  
Solid State Reactions ◽  
Platinum Resistance ◽  
Platinum Resistance Thermometers ◽  
Resistance Thermometers ◽  
Kinetics Of

AbstractWe have studied the kinetics of the solid-state amorphizing reaction in thin film multilayers of Ni and Zr. Crystalline Ni and Zr films were deposited in ultra-high vacuum onto platinum resistance thermometers embedded in alumina. An electronic feedback circuit controls the temperature of the substrata by adjusting the power dissipated by the platinum resistors. We find that structural relaxation in the asdeposited Ni and Zr films affects the initial stages of the reaction. For long reaction times there is a discontinuous change in the reaction rate. The time to reach this transition increases with film thickness and depends exponentially on 1/T, with an apparent activation energy of 3 eV atom−1.

XPS, AES and Leed Studies of The Interaction Between The Si(100) 2×1 Surface and Cadmium Deposited at Room Temperature

1995 ◽  
Vol 382 ◽  
Author(s):  
S. Santucci ◽  
S. Di Nardo ◽  
L. Lozzi ◽  
M. Passacantando ◽  
P. Picozzi
Keyword(s):  
Photoelectron Spectroscopy ◽  
Room Temperature ◽  
Thermal Evaporation ◽  
Early Stage ◽  
High Vacuum ◽  
Amorphous Structure ◽  
Ultra High Vacuum ◽  
Energy Position ◽  
X Ray

ABSTRACTVery thin films of cadmium, with a mean thickness between 1 Å and 500 Å, were deposited by thermal evaporation in ultra-high-vacuum on a Si(100) 2×1 surface held at room temperature. In situ X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy were performed in order to investigate the interaction between the silicon substrate and the deposited cadmium. In samples with deposited mean thickness up to 3 Å, cadmium and silicon are found to be strongly interacting. In fact both XPS and AES spectra show evident changes in shape and energy position leading to the conclusion that a chemical compound between Cd and Si is formed. No diffusion between cadmium and silicon is observed, so the cadmium atoms deposited after the first 3 Å show a bulk character. The analysis of the first derivative intensity of the Si L23VV and Cd M5N45N45 Auger signals, varying the amount of deposited Cd, indicates the formation of islands in the early stage of the Cd growth. These islands show an amorphous structure as observed by using the LEED spectroscopy.

Structure of Palladium Single-Crystal Films Prepared by Flash Evaporation onto (001) NaCl Substrates

1970 ◽  
Vol 28 ◽  
pp. 456-457
Author(s):  
L. E. Murr ◽  
G. Wong
Keyword(s):  
Single Crystal ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
High Rate ◽  
Flash Evaporation ◽  
Optimum Load ◽  
Single Crystal Films ◽  
Crystal Films ◽  
A Current

Palladium single-crystal films have been prepared by Matthews in ultra-high vacuum by evaporation onto (001) NaCl substrates cleaved in-situ, and maintained at ∼ 350° C. Murr has also produced large-grained and single-crystal Pd films by high-rate evaporation onto (001) NaCl air-cleaved substrates at 350°C. In the present work, very large (∼ 3cm2), continuous single-crystal films of Pd have been prepared by flash evaporation onto air-cleaved (001) NaCl substrates at temperatures at or below 250°C. Evaporation rates estimated to be ≧ 2000 Å/sec, were obtained by effectively short-circuiting 1 mil tungsten evaporation boats in a self-regulating system which maintained an optimum load current of approximately 90 amperes; corresponding to a current density through the boat of ∼ 4 × 104 amperes/cm2.

Hetero-Epitaxy of Group Va Metals on Sapphire

1972 ◽  
Vol 30 ◽  
pp. 492-493
Author(s):  
J. E. O'Neal ◽  
J. J. Bellina ◽  
B. B. Rath
Keyword(s):  
Thermal Contact ◽  
High Vacuum ◽  
Electron Beam Evaporation ◽  
Ultra High Vacuum ◽  
Backing Plate ◽  
Sapphire Substrates ◽  
Deposition Parameters ◽  
Polishing Damage ◽  
Reflection Electron Diffraction

Thin films of the bcc metals vanadium, niobium and tantalum were epitaxially grown on (0001) and sapphire substrates. Prior to deposition, the mechanical polishing damage on the substrates was removed by an in-situ etch. The metal films were deposited by electron-beam evaporation in ultra-high vacuum. The substrates were heated by thermal contact with an electron-bombarded backing plate. The deposition parameters are summarized in Table 1.The films were replicated and examined by electron microscopy and their crystallographic orientation and texture were determined by reflection electron diffraction. Verneuil-grown and Czochralskigrown sapphire substrates of both orientations were employed for each evaporation. The orientation of the metal deposit was not affected by either increasing the density of sub-grain boundaries by about a factor of ten or decreasing the deposition rate by a factor of two. The results on growth epitaxy are summarized in Tables 2 and 3.

An in situ and ex situ TEM study of the formation of thin cobalt silicide films by molecular beam epitaxy on the silicon (100) surface

1988 ◽  
Vol 46 ◽  
pp. 884-885
Author(s):  
D. Loretto ◽  
J. M. Gibson ◽  
S. M. Yalisove ◽  
R. T. Tung
Keyword(s):  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
Defect Density ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Ex Situ ◽  
Metal Base ◽  
In Situ Experiments ◽  
Potential Applications

The cobalt disilicide/silicon system has potential applications as a metal-base and as a permeable-base transistor. Although thin, low defect density, films of CoSi2 on Si(111) have been successfully grown, there are reasons to believe that Si(100)/CoSi2 may be better suited to the transmission of electrons at the silicon/silicide interface than Si(111)/CoSi2. A TEM study of the formation of CoSi2 on Si(100) is therefore being conducted. We have previously reported TEM observations on Si(111)/CoSi2 grown both in situ, in an ultra high vacuum (UHV) TEM and ex situ, in a conventional Molecular Beam Epitaxy system.The procedures used for the MBE growth have been described elsewhere. In situ experiments were performed in a JEOL 200CX electron microscope, extensively modified to give a vacuum of better than 10-9 T in the specimen region and the capacity to do in situ sample heating and deposition. Cobalt was deposited onto clean Si(100) samples by thermal evaporation from cobalt-coated Ta filaments.

Nucleation and initial growth of Pd2Si crystals on Si(111)

1993 ◽  
Vol 51 ◽  
pp. 844-845
Author(s):  
Xianghong Tong ◽  
Oliver Pohland ◽  
J. Murray Gibson
Keyword(s):  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Initial Growth ◽  
Surface And Interface ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Initial Stage ◽  
Effect Of Surface

The nucleation and initial stage of Pd2Si crystals on Si(111) surface is studied in situ using an Ultra-High Vacuum (UHV) Transmission Electron Microscope (TEM). A modified JEOL 200CX TEM is used for the study. The Si(111) sample is prepared by chemical thinning and is cleaned inside the UHV chamber with base pressure of 1x10−9 τ. A Pd film of 20 Å thick is deposited on to the Si(111) sample in situ using a built-in mini evaporator. This room temperature deposited Pd film is thermally annealed subsequently to form Pd2Si crystals. Surface sensitive dark field imaging is used for the study to reveal the effect of surface and interface steps.The initial growth of the Pd2Si has three stages: nucleation, growth of the nuclei and coalescence of the nuclei. Our experiments shows that the nucleation of the Pd2Si crystal occurs randomly and almost instantaneously on the terraces upon thermal annealing or electron irradiation.

Transmission Electron Microscopy of Epitaxial silicides grown by ultra high vacuum deposition

1989 ◽  
Vol 47 ◽  
pp. 462-463
Author(s):  
D. Loretto ◽  
J. M. Gibson ◽  
S. M. Yalisove
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Diffraction ◽  
High Vacuum ◽  
High Energy ◽  
Energy Electron ◽  
Ultra High Vacuum ◽  
Ex Situ ◽  
Transmission Electron

The silicides CoSi2 and NiSi2 are both metallic with the fee flourite structure and lattice constants which are close to silicon (1.2% and 0.6% smaller at room temperature respectively) Consequently epitaxial cobalt and nickel disilicide can be grown on silicon. If these layers are formed by ultra high vacuum (UHV) deposition (also known as molecular beam epitaxy or MBE) their thickness can be controlled to within a few monolayers. Such ultrathin metal/silicon systems have many potential applications: for example electronic devices based on ballistic transport. They also provide a model system to study the properties of heterointerfaces. In this work we will discuss results obtained using in situ and ex situ transmission electron microscopy (TEM).In situ TEM is suited to the study of MBE growth for several reasons. It offers high spatial resolution and the ability to penetrate many monolayers of material. This is in contrast to the techniques which are usually employed for in situ measurements in MBE, for example low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED), which are both sensitive to only a few monolayers at the surface.

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